Cyanuric Acid Health Concerns

[kbaumann]

I was told a state, I think PA, has made certain laws against the use of cyanuric acid CYA. I dont know this to be true in the least but wanted to dig a little deeper. I wanted to ask you all if there is anything you know that is considered neagative to peoples health by using CYA. ~ Karl

[chem geek]

Karl,

I believe you are referring to the information in this link. Though they are right about CYA's effect on chlorine effectiveness, they have gone overboard in saying to use none in indoor pools or in spas. The chlorine will be too strong in your spa if you use it without CYA and it will degrade your hot tub cover quite a bit faster since the average effective chlorine level will be 6 times higher or so without the CYA. There are no laws governing residential pool or spa use with regard to CYA. They only regulate chemical usage in commercial/public pools/spas. New York has banned CYA use in commercial/public pools and spas, again from a lack of clear education, though I think they passed that law after the Milwaukee cryptosporidium incident.

Unfortunately, governments sometimes overreact without going to the core science as described in this paper so when something goes wrong at a high CYA level, for example, they ban CYA instead of regulating its quantity. In fact, there may be a significant reduction in nitrogen trichloride production from lower active chlorine levels you can achieve by using CYA as I describe in this post.

CYA itself is not harmful at dosages and exposure levels in pools/spas (see test studies here) and does not absorb through the skin (see here).

Richard

[kbaumann]

So it seems the reason PA Department of Health doesn’t want to use CYA isn’t because it is harmful to health within itself but because "At even moderate levels of cyanuric acid, the amount of time it takes chlorine to kill pseudomonas aeruginosa (the bacteria that causes “hot tub itch”) can be as much as a hundred times as long as in a hot tub or spa without cyanuric acid. For this reason, the Pennsylvania Department of Health does not recommend the use of cyanuric acid or stabilized chlorine in any hot tubs or spas."

If that is the reason, then doesn’t the 12ppm shocking recommended in a spa with 30ppm CYA take care of this "kill" problem? It seems to me that all we are doing with the CYA in the water is compensating by adding more Free Chlorine (FC) to have the right sanitation... So why don’t we forget about the CYA and just add a lower dose of chlorine to get the same effect? And if it is because of the chlorine tearing up the cover and spa components without having the CYA, then are we not still doing this by increasing the Free Chlorine (FC) because of the CYA? I pray you are following me on this thought process! Typing isnt my strong suit! ~ Karl

[chem geek]

If you could consistently maintain 0.2 ppm FC in commercial/public pools (0.05 to 0.1 ppm FC in residential pools) and 0.6 ppm FC in spas even during significant bather load or in the presence of sunlight, then you would be right that you wouldn't need the CYA. However, even localized demand can use up chlorine locally and certainly in sunlight half the chlorine can break down every 35 minutes. So in practice it is easier to use CYA, but to not overuse it, and to have the FC higher to compensate for the CYA effect. The higher FC then provides a larger reserve of chlorine so that you do not run out.

At hot spa temperatures, 4 ppm FC with 30 ppm CYA is equivalent to 0.64 ppm FC with no CYA. At pool temperatures, 3 ppm FC with 30 ppm CYA is equivalent to 0.085 to 0.18 ppm FC with no CYA (depending on temperature of the pool). These levels are still fast enough to kill bacteria very quickly in around 1 minute for a 99% kill in pools and less than 10 seconds in spas (the level is set higher in spas to be conservative due to Pseudomonas aeruginosa which is the bacteria that causes hot tub itch/rash and can relatively quickly form biofilms so you want to kill it before it does so).

Since the active chlorine (hypochlorous acid) concentration is proportional to the FC/CYA ratio, the net effect on the killing rates for pathogens, the oxidation rates of bather waste, and the effects on swimsuits, skin, hair, materials in pools and spas, etc. are all the same as if the FC were very low and there were no CYA. The only time when the FC itself comes into play is if you were to drink or otherwise ingest the chlorinated water directly since then the chlorine will all ultimately get released.